I
NSTRUMENT
C
ONFIDENCE
C
HECK
Electronic Copy of LTI’s UltraLyte User’s Manual – 7
th
Edition June 1998
48
Instrument Confidence Check
The measurement accuracy of a lidar instrument can
be verified by several methods. Verifying it directly,
however—by measuring the velocity of an object
traveling at a known speed—is seldom practical.
And the nature of lidar is such that it cannot be
tricked by a vibrating object, such as a tuning fork,
into displaying a velocity. For those reasons, LTI has
designed two passive test procedures.
The tests are the
fixed distance check
and the
delta
distance check.
The point of the tests is to verify the
accuracy of the two key elements of lidar speed
measurement: precise time measurements and the
ability to make mathematical calculations.
LTI recommends that one of the tests be performed
on the instrument each time it is taken on duty.
Regardless of which test you intend to perform, we
also suggest a test area be permanently installed in
a convenient location.
The test area must establish permanent, known
distances between a target and a shooting mark
(fixed distance test) or between two targets and a
shooting mark (delta distance test). The targets and
the shooting mark must form a straight line. Keep in
mind that the minimum measurement distance for
these tests is 50 feet.
A target can be any flat, permanent structure—a
sign or wall, for example—painted with a bull’s eye
or other aiming point. The shooting mark is where an
operator stands to conduct the test, and can be an X
painted on the pavement.
Testing and test-area specifics are discussed below.
There are two things you should note, however.
First, the distances specified are
horizontal
distances. (A horizontal distance is measured along
a straight and level path from the shooting mark to
the center of the aiming point.)
For Internal Use Only. Not for Distribution.
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